Short answer: it depends on what you're practicing.
Long answer: it depends on who you are, what you're trying to build, and which phase of learning you're in.
The case against music during drilling
When you're learning or fixing a technical pattern — a new grip, a different takeback, a corrected contact point — you need access to your proprioceptive feedback. You need to feel what your body is doing. Music, especially music you like, pulls your attention outward. It fills the space that feedback needs to occupy.
I generally ask students learning something new to practice without music for the first few weeks. Not because music is bad, but because the skill acquisition phase requires a different kind of attention than maintenance practice.
The case for music during conditioning
Mindless footwork ladders. Ball machine sessions. Fitness circuits between practices. These are different. Here, music is documented to improve performance — it raises your mood, moderates your perception of effort, and keeps you moving when boredom would otherwise win.
My on-court warmup playlist is high BPM specifically for this reason. I'm not learning anything during a warmup — I'm raising my heart rate and loosening my movement. Music helps.
The case for music during match play simulation
This one's more interesting. Some coaches argue you should practice under conditions that simulate match pressure — which means no music, because there's no music during a match. I agree with this for advanced players preparing for competition. For recreational players, I'm less rigid about it.
What I actually do
During my own practice: no music for technical work, playlist for fitness, silence for match simulation.
With students: I'll usually ask them to take out the earbuds when we're working on something specific. During free hitting or physical drills, I'll sometimes let them choose. I've learned not to fight it too hard — a student who's engaged with music in is better than a student who's disengaged without it.
The goal is always the same: attention on the right thing at the right time.